As is well known, there is a need to develop methods that increase or optimize the productivity of animals to enhance food production. Not only does the producer benefit by lower costs of production but the consumer benefits ultimately from increased supplies of meat and animal products at a lower cost.
For approximately the last 35 years, antibiotics such as penicillin, the tetracyclines, and bacitracin have enabled benefits to both producer and consumer by enhancing growth and/or improving feed conversion in animals, most effectively in poultry and swine.
Benefits from incorporating antibiotics into animal feeds are usually attributed to their minimizing the deleterious effects of pathogenic microorganisms in the gastrointestinal tract of the host. Evidence for the induction of antibiotic-resistant microorganisms and concern for their possible transfer to and infection of humans have generated broad searches for compounds that will improve animal performance without substantially impinging on human health concerns.